Jean-Louis Vincent: eb. This article has been cited by other articles in PMC. Abstract Cardiac output is the amount of blood the heart pumps in 1 minute, and it is dependent on the heart rate, contractility, preload, and afterload. Open in a separate window. Figure 1. Four determinants of cardiac output, using an analogy to the speed of a bicycle.
The analogy and the four determinants of cardiac output Heart rate The heart rate is perhaps the simplest determinant of cardiac output to visualize: the faster the heart beats, the more blood can be pumped over a particular period of time.
Preload Preload is the degree of myocardial distension prior to shortening. Afterload Afterload is the force against which the ventricles must act in order to eject blood, and is largely dependent on the arterial blood pressure and vascular tone.
Some clinical applications Myocardial depression of sepsis Sepsis is usually associated with a normal or high cardiac output; yet many studies have shown that myocardial depression can occur even early in the course of sepsis [ 1 ], so why is cardiac output not reduced?
Deleterious effects of inotropic therapy As the long-distance cyclist will know, prolonged strenuous exercise can lead to high tissue oxygen demands, which can later result in impaired muscle contraction and poor performance. Beneficial effects of vasodilating substances Arterial vasodilator therapy results in significant improvements in cardiac output in patients with heart failure by reducing afterload cycling downhill.
Potentially harmful effects of vasopressor agents In contrast to the beneficial effects of vasodilator drugs, the administration of strong vasopressors may decrease cardiac output by increasing afterload, even in individuals with normal cardiac function. Effects of inodilating substances Some drugs, such as phosphodiesterase inhibitors milrinone, enoximone and levosimendan, exert some inotropic effects in addition to vasodilating effects. Effects of fluid administration Fluid administration takes advantage of the Frank—Starling relationship to increase stroke volume and cardiac output.
Effects of calcium entry blockers on cardiac output As calcium is essential to myocardial contraction, calcium entry blockers are expected to decrease the force of contraction of the myocardium.
Conclusion The interpretation of cardiac output is not as straightforward as it may seem at first glance. Competing interests The author declares that they have no competing interests. The cardiovascular response of normal humans to the administration of endotoxin. N Engl J Med. Circ Res. Effect of oral milrinone on mortality in severe chronic heart failure. Treatment of severe heart failure: quantity or quality of life? A trial of enoximone. Enoximone Investigators. Br Heart J.
Effect of vasodilator therapy on mortality in chronic congestive heart failure. The same principle applies in the body with blood and the vessels. If the area available for blood to flow through is reduced then pressure will increase. If pressure remains very high for long periods of time the danger of a vessel bursting increases significantly, in the case of the aorta this would result in a virtually instantaneous death through massive immediate blood loss.
The major concern with a BP that is consistently elevated is that there may be a potential obstruction within the blood vessel which narrows the available area blood has to flow through. This is pictured on the adjacent diagram. A diet high in fat, low in vegetables and a sedentary lifestyle can all contribute to the build up of these fatty plaques. If the blockage is not cleared quickly then the tissues that receive oxygen and nutrients from that vessel are likely to die.
Depending on where the blockage occurs the effects can range from minor to fatal. If the blockage occurs in the coronary heart arteries then a heart attack usually fatal will result, if the blockage occurs in a cerebral brain blood vessel then a stroke will occur with usually irreversible damage to the part of the brain that is effected. Blood vessels can also narrow when stress hormones e. This can occur when someone is very stressed or has a lot of tightened muscles due to exercise stress, as can be seen in the adjacent picture.
As BP is a key measure of the health of the cardiovascular system it should be measured regularly and people whose readings are consistently elevated at rest should be treated accordingly, usually by referral to medical personnel, restriction of exercise to low intensity and a focus on dietary and lifestyle modifications to reduce stress and the intake of fatty foods. Make writing personal training programs easy with these custom designed exercise templates, and keep your clients focused and progressing.
Pain-free clients are happy clients. Claim your free copy of the client back care guide today. Your clients will thank you for it! In the middle is the BSA or m squared column. You use a square edge to draw a line from left column to the right column passing over BSA. This is the BSA.
Francis Abraham Useful information. Worth reading. Anthony Cardiology Journal Great site. Lovely committed work of true fan s. All the very best. Thanks for the information. Topic Overview For the body to function properly, the heart needs to pump blood at a sufficient rate to maintain an adequate and continuous supply of oxygen and other nutrients to the brain and other vital organs.
What is a normal cardiac output? When does the body need a higher cardiac output? Why is maintaining cardiac output so important? Related Information Heart Failure. Normal physiology of the cardiovascular system. In V Fuster et al. New York: McGraw-Hill.
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